Butterfly valve having a function for measuring a flow rate and method of measuring a flow rate with a butterfly valve

ABSTRACT

A butterfly valve having a function for measuring a flow rate of a fluid flowing through the butterfly valve includes a main body, a valve shaft fixed rotatably to the main body, a valve member fixed to the valve shaft and mounted rotatably in the main body, a valve opening detection device for detecting a valve opening of the butterfly valve, and a torque detection device for detecting a dynamic torque applied to the valve member around the valve shaft by the fluid.

BACKGROUND OF THE INVENTION

The present invention relates to a butterfly valve and, moreparticularly, to a butterfly valve having a function for measuring aflow rate of a fluid flowing through the butterfly valve. The inventionis also concerned with a method of measuring a flow rate with abutterfly valve, as well as a method of controlling a flow rate with abutterfly valve.

In general, a butterfly valve has a valve member which is rotatablymounted in a main body and fixed to a valve shaft which is fixedrotatably to the main body. The valve shaft is operated from outside ofthe main body manually or by means of a pneumatic or electric actuatorso as to rotate the valve member, thus changing the valve opening.

The flow rate of a fluid flowing through such a butterfly valve can becontrolled by measuring the flow rate by a measuring means and changingthe valve opening based on the measured flow rate.

Such a measurement of the flow rate is conducted by, for example, aflowmeter which is independent from the butterfly valve and installed inthe vicinity of the butterfly valve. In this case, the flow ratemeasured by this flowmeter is regarded as the flow rate of the fluidflowing through the butterfly valve.

A typical flowmeter used for this purpose is a differential pressuretype flowmeter comprises an orifice provided in the pipe in which thebutterfly valve is installed, and a pressure sensor capable of detectingthe differential pressure across the orifice, i.e., between the upstreamand downstream sides of the orifice. The flow rate is determined fromthe detected pressure ΔP and a capacity coefficient, (Cv value) which isa constant value peculiar to the orifice and determined beforehandthrough, for example, an experiment.

As a modification of such a differential pressure type flowmetercomposed of an orifice and a pressure sensor, in order to attain acompact construction of the system, there is a combustion system whichmakes use of the butterfly valve itself as such an orifice. Namely, sucha combination system comprises a pressure sensor capable of detectingthe differential pressure of the fluid across the butterfly valve andmeans for detecting the valve opening of the butterfly valve. A capacitycoefficient (Cv value) as function of the valve opening peculiar to thisbutterfly valve is beforehand determined through, for example, anexperiment. Thus, the flow rate is determined from the detecteddifferential pressure ΔP and the value of the capacity coefficient Cvcorresponding to the detected valve opening. This combination system isproposed in Japanese Patent Unexamined Publication No. 62-270873 of thesame applicant.

Another combination system similar to the above-mentioned combinationsystem of a butterfly valve and a pressure sensor is disclosed inJapanese Utility Model Unexamined Publication No. 62-1117, which isdesigned to measure the flow rate of a fluid flowing through a gatevalve used also as such an orifice. Thus, this combination systemcomprises a pressure sensor capable of detecting the differentialpressure across the gate valve, and means for detecting the valve liftof the gate valve. A capacity coefficient (Cv value) as a function ofthe valve lift peculiar to this gate valve is beforehand determinedthrough, for example, an experiment. Thus, the flow rate is determinedby the detected differential pressure ΔP and the value of the capacitycoefficient Cv corresponding to the detected valve lift.

Flowmeters of types other than the above mentioned differential pressuretype also has been used. For instance, a system has been known in whichthe valve opening of a butterfly valve disposed in a line of aconductive fluid is controlled in accordance with the flow rate of thefluid measured by an electromagnetic flowmeter disposed independently inthe vicinity of the butterfly valve.

In general, it has been regarded that the torque required for rotatingthe valve member and for fixing the same with a desired valve opening ispreferably small, because the smaller torque requires a smaller externaldriving torque and, hence, a smaller actuator. The smaller torque ispreferred also from the view point of maneuverability.

From this point of view, intense study and development have been madefor the purpose of reducing the dynamic torque applied to the valvemember around the valve shaft by the fluid flowing through the butterflyvalve. For instance, the same applicant has proposed, in Japanese PatentUnexamined Publication Nos. 55-142169 and 56-28355, butterfly valvesequipped with seat rings capable of reducing the external drivingtorque.

Known butterfly valves, including those described hereinbefore, functiononly as a restriction in which the valve member restricts the flow ofthe fluid.

Thus, in order to enable a butterfly valve to regulate or control theflow rate, it is necessary to install suitable means for measuring theflow rate in the path of the flow of the fluid in addition to the valvemember. A butterfly valve system including such means for measuring theflow rate therefore complicates the construction of the flow passage,failing to meet the demand for a compact design.

It is also to be pointed out that quantitative and time deviations tendto exist between the flow rate measured by the flowmeter and the actualflow rate through the butterfly valve, due to the fact that the flowrate is measured indirectly or at a position which is spaced from thebutterfly valve. This makes it difficult to measure and, hence, tocontrol the flow rate accurately.

SUMMARY OF THE INVENTION

Accordingly, the present invention aims at providing a butterfly valvewhich has, in addition to the function as a restriction, a function ofmeasuring the flow rate.

More specifically, a first object of the present invention is to providea butterfly valve in which the valve member and the valve shaft functionas a sensor for measuring the flow rate.

A second object of the present invention is to provide a method ofmeasuring flow rate of a fluid flowing through a butterfly valve,wherein the valve member and the valve shaft of the butterfly valvefunction as a sensor.

The first object of the present invention can be achieved by a butterflyvalve having a function for measuringf a flow rate of a fluid flowingthrough said butterfly valve, comprising;

a main body,

a valve shaft fixed rotatably to said main body,

a valve member fixed to said valve shaft and mounted rotatably in saidmain body,

a valve opening detection means for detecting a valve opening of saidbutterfly valve, and

a torque detection means for detecting a dynamic torque applied to saidvalve member around said valve shaft by said fluid.

The second object of the present invention can be achieved by a methodof measuring a flow rate of a fluid flowing through a butterfly valve,comprising the steps of;

detecting a valve opening of said butterfly valve,

detecting a dynamic torque applied to said valve member around saidvalve shaft by said fluid, and

determining said flow rate as a function of said detected valve openingand said detected dynamic torque.

According to an experiment conducted by the present inventor, it isshown that the flow rate of a fluid flowing through a butterfly valvecan be substantially definitely determined by the valve opening, thedynamic torque applied to the valve member around the valve shaft by thefluid and a characteristic peculiar to each butterfly valve, providedthat the measurement is conducted on the same fluid under the samecondition.

Consequently, in the butterfly valve of the present invention, since thevalve opening is detected by the valve opening detection means, andsince the dynamic torque applied to the valve member around the valveshaft by the fluid is detected by the torque detection means, once therelationship of the flow rate to the valve opening and the dynamictorque peculiar to each butterfly valve is beforehand obtained, it ispossible to determine the flow rate from the detected valve opening andthe detected dynamic torque.

In general, the flow rate of a fluid flowing through a butterfly valveis ruled by the differential pressure across the butterfly valve, i.e.,between the upstream and downstream sides of the butterfly valve, andthe characteristic which is peculiar to the butterfly valve, providedthat the type of the fluid and the flowing conditions are unchanged.Thus, the flow rate Q can be expressed as the following formula (1) as afunction F of variants θ (valve opening) and ΔP (differential pressure).

    Q=F(θ, ΔP)                                     (1)

The function F is determined in accordance with factors such as thediameter of the valve member, configuration of the valve member and soforth. It will be naturally understood that the value of the function Fincreases as one or both of the valve opening θ and the differentialpressure ΔP increase. Therefore, once the function F peculiar to eachbutterfly valve is determined through an experiment or through atheoretical analysis, the flow rate Q can be definitely determined foreach butterfly valve by measuring the valve opening θ and thedifferential pressure ΔP and substituting the measured values to thepredetermined function F.

The attention of the present inventor is drawn to the fact that thedynamic torque applied to the valve member around the valve shaft by thefluid varies in accordance with the change in the flow rate. Adiscussion will be therefore given as to a function G of the followingformula (2) which employs the valve opening θ and the dynamic torque Tas the variances, as an alternative or a substitution for theaforementioned function F.

    Q=G(θ, T)                                            (2)

In order to evaluate this function, the present inventor conducts anexperiment having the following steps (i) to (vii).

(i) To apply a desired differential pressure ΔP to the butterfly valve.

(ii) To measure the opening θ, the torque T and the flow rate Q f thefluid flowing through the butterfly valve.

(iii) To measure and record changes in the torque T and the flow rate Qcaused by a change in the differential pressure ΔP with the opening θbeing fixed.

(iv) To conduct the same measurement and record as (iii) by varying theopening θ by a suitable angle Δθ.

(v) To repeatedly execute measurement and record of the steps (iii) and(iv) while varying the opening θ from 0° to 90° at an interval of Δθ.

(vi) To execute, as necessitated, steps (i) to (v) for various kinds offluids.

(vii) To execute steps (i) to (vi) for a plurality of butterfly valves.

It can be known from the result of the experiment consisting of thesteps (i) to (vii) that the function G practically comes into existence.Accordingly, the function G as the characteristic peculiar to eachbutterfly valve can be determined in the form of an experimentalformula, by filling lack of data through a suitable interpolation methodor by employing a suitable approximation expression.

Consequently, by using this peculiar function G, it is possible todefinitely determine the flow rate Q of a fluid flowing through thebutterfly valve, by measuring the valve opening θ and the dynamic torqueT, without requiring meaasurement of the differential pressure ΔP.

A theoretical explanation will be given as to the existence of thefunction G and the practical determination of the function G.

In general, it is known about the butterfly valve that a functionalrelationship exists between the valve opening θ and the Cv value(capacity coefficient of the butterfly valve) which is a function ofvariances Q (flow rate) and ΔP (differential pressure).

There also exists a functional relationship between the valve opening θand the Cu value (practical torque coefficient) which is a function ofvariances T (dynamic torque) and ΔP (differential pressure).

Thus, the Cv value and the Cu value are respectively expressed by afunction f of variants Q and ΔP, and a function g of vaiants T and ΔP asshown in the following formulae (3) and (4).

    Cv=f(Q, ΔP)                                          (3)

    Cu=g(T, ΔP)                                          (4)

Assuming that the conditions as shown in the following formulae (5) and(6), in which the Cv value and the Cu value are respectively expressedby a function ff of variant θ and a function gg of variant θ, are met,

    Cv=f f(θ)                                            (5)

    Cu=g g(θ)                                            (6)

the following formula (7), in which the flow rate Q is expressed by afunction f of variants Cv and ΔP, is derived from the formulae (3) and(5),

    Q=f(Cv, ΔP)→f(ff(θ), ΔP)          (7)

and the following formula (8), in which the pressure ΔP is expressed bya function g' of variants Cu and T, is derived from the formulae (4) and(6).

    ΔP=g'(Cu, T)=g'(gg(θ), T)                      (8)

Then, the following formula (9), in which the flow rate Q is expressedby a function K of variants T and θ, is derived from the formulae (7)and (8).

    Q=h(ff(θ), g'(gg(θ), T))=K(T,θ)

(9)

Whereby, it can be seen that the formula (9) thus obtained is equivalentto the formula (2): namely, the function K and the function G areidentical. Thus, the experiment conducted by the present invention ismaterially equivalent to the confirmation of a fact that the assumptionsof the formulae (5) and (6) are practically correct and to thedetermination of the functions ff(θ) and gg(θ) in the formulae (5) and(6).

Preferably, the butterfly valve of the present invention has an actuatorfor rotating the valve member. Such an actuator will enable the valvemember to be rotated and fixed with a torque which is much greater thanthat exerted by a manual labor.

It is also preferred that the butterfly valve of the present inventionhas a flow rate computation means for computing the flow rate of a fluidas a predetermined function of the valve opening and the dynamic torque.Such a flow rate computation means can automatically output the computedflow rate.

More preferably, the butterfly valve of the present invention has boththe actuator and the flow rate computation means. In such a case, it ispreferred that the butterfly valve also has a control means at which adesired flow rate can be externally set and which instructs the actuatorto rotate the valve member such that the computed flow rate approachesthe desired flow rate. In such a case, the flow rate can be controlledwithout delay through a feedback of the measured data. Preferably, thecontrol means is adapted such that the desired flow rate can be set tothe control means from a remote place by a remote operation meansthrough a suitable tele-communication means.

The actuator used in the butterfly valve of the present invention ispreferably an electric actuator, a pneumatic actuator, a diaphragm-typeactuator or a solenoid-type actuator.

The torque detection means used in the butterfly valve of the presentinvention preferably includes a strain detector provided to the valveshaft, and more preferably such a strain detector comprises a straingauge attached on the valve shaft.

It is also preferred that the valve opening detection means used in thebutterfly valve of the present invention includes an angle sensorconnected to the valve shaft. In such a case, the angle sensorpreferably comprises a potentiometer or a rotary encoder.

The butterfly valve of the present invention can be designed either as aso-called central-type valve in which the valve member is fixed to thevalve shaft at a central axis of the valve member, or so-called aneccentric-type valve in which the valve member is fixed to the valveshaft at an eccentric axis of the valve member.

The function of the valve opening and the dynamic torque used in themethod of the present invention is preferably estimated through anexperiment. In such a case, the function can be estimated for any typeof butterfly valves.

The estimation of the function through the experiment may be based on anassumption that a linear proportional relationship exists between thedynamic torque and the flow rate when the valve opening is fixed. Insuch a case, the experiment and the estimation can be simplified.

The method of the invention for determining the flow rate may employ achart which shows the flow rate values in relation to the valve openingand the dynamic torque. Such a chart is preferably obtained through anexperiment.

The determination of the flow rate in the measuring method of thepresent invention can be performed rapidly and easily when a suitablecomputer is used.

It is also preferred that the butterfly valve is controlled such thatthe flow rate determined by the measuring method of the presentinvention approaches the desired flow rate which can be externally set.In such a case, a rapid control of the flow rate can be realized througha feedback of the measured data.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partly-sectioned perspective view of a portion of anembodiment of the butterfly valve according to the present invention;

FIG. 1A is a schematic view of an eccentric-type valve member inaccordance with another embodiment of the invention.

FIG. 2 is a schematic diagram of an embodiment of the present invention;

FIGS. 3 to 6 are graphs showing the functions used in the presentinvention;

FIG. 7 is schematic diagram of a system used in an experiment conductedon an embodiment of the present invention;

FIGS. 8 and 9 are graphs showing the result of the experiment; and

FIGS. 10 and 11 are graphs showing the functions derived from theresults of experiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of the present invention will be described withreference to the accompanying drawings.

Referring to FIG. 1 illustrating an embodiment of the butterfly valve inaccordance with the present invention, the butterfly valve has a mainbody 1 and a valve member 2 having an outside diameter slightly smallerthan the inside diameter of the main body 1. The valve member 2 isrotatably supported in the main body 1 by means of a valve shaft 3. Inthe illustrated embodiment, the arrangement of the valve member 2 to thevalve shaft 3 is so-called central-type in which the valve member 2 isfixed to the valve shaft 3 at the central axis of the valve member 2.This, however, is only illustrative and the arrangement may be so-calledeccentric type in which the valve member 2A is fixed to the valve shaft3A at the eccentric axis of the valve member 2 as shown in FIG. 1A. Thevalve shaft 3 extends through a shaft bore formed in the main body 1. Agland packing 7 and a seal ring 8 are disposed between the valve shaft 3and the wall of the shaft bore, in order to provide a seal therebetweenwhile allowing the valve shaft 3 to rotate with respect to the mainbody 1. A smooth rotation of the valve shaft 3 is ensured by a shaftbearing 6.

The main body 1 of this butterfly valve is connected to a pipe 100 in amanner known per se as shown in FIG. 2. The pipe 100 is usually made ofa metal or a plastic and the diameter of the pipe 100 generally rangesbetween several millimeters and several meters. Preferably, the diameterof the pipe 100 ranges between more than 10 millimeters and severalmeters, more preferably between several tens of millimeters and severalmeters. Usually, a plurality of classes of bufferfly valve havingdifferent sizes of the main body 1 are manufactured and the size of themain body 1 of which conforms with the pipe diameter is used. Ingeneral, a greater inside diameter of the pipe 100, the main body 1 andthus valve member 2, a greater dynamic torque as a signal is applied tothe valve member 2 around the valve shaft 3 by the fluid. Therefore, theprecision of the flow rate measurement is increased more easily when theinside diameters of the pipe 100 and the main body 1 are greater.Conversely, the dynamic torque as the signal becomes smaller as the sizeof the main body 1, i.e., the size of the valve member 2, becomessmaller, thus, in order to enhance the precision of the measurement,therefore, it is preferred to reduce the levels of noises such aselectric noises. A higher degree of conformity between the insidediameter of the pipe 100 and the inside diameter of the main body 1reduces any turbulency of flow of the fluid which is generated at thejuncture between the pipe 100 and the main body 1. In such a case, thestate of the flow of fluid coming into the main body 1 more closelyapproximates the state of laminar flow. This feature is advantageousparticularly in the measurement of large flow rates.

In the illustrated embodiment, since the outside diameter of the valvemember 2 is slightly smaller than the inside diameter of the main body1, the flow passage is not completely shut off even when the valveopening is 0°. The butterfly valve of the invention, however, may have aseat ring or an "O" ring made of rubber. Teflon [Trade name] or metaletc. on the inner peripheral surface of the main body 1 so as to becontacted by the peripheral edge of the valve member 2 thereby tocompletely shut off the flow of the fluid when the valve opening is 0°.The arrangement also may be such that another butterfly valve or anotherkind of valve which can completely close the flow passage is disposed inthe pipe 100 in series to the butterfly valve of the present invention.

An actuator 11 shown in FIG. 2 is operatively connected to one end 9 ofthe valve shaft 3 in a manner known per se. The actuator 11 is capableof rotating the valve shaft 3 so as to cause the valve member 2 torotate about the axis of the valve shaft 3. The actuator 11 is alsocapable of fixing the valve shaft 3 and, hence, the valve member 2 at apredetermined angle, thus determining the valve opening of the butterflyvalve. Various types of actuators such as an electric actuator, apneumatic actuator, a diaphragm actuator and a solenoid-type actuatorcan be used as the actuator 11. The use of the actuator 11 is notessential. Namely, the butterfly valve of the invention may beconstructed such that the valve shaft 3 is rotated manually.

A strain detector 12 capable of detecting a minute twist of the valveshaft 3 is provided on the valve shaft 3. A known strain gauge ispreferably used as the strain detector 12. The amount of twist detectedby the strain detector 12 is delivered to a torque converter 13 whichconverts the detected amount of the twist into the dynamic torque whichacts on the valve member 2 tending to rotate the valve member 2 aboutthe axis of the valve shaft 3, and outputs the thus determined value ofdynamic torque.

The strain detector 12 and the torque converter 13 in combinationprovide a torque detection means 14. Various other torque detectors canbe used as the means for detecting the dynamic torque applied to thevalve member 2 around the valve shaft 3 by the fluid. It is thereforepossible to use an optimum dynamic torque detector taking into accountboth the measurement precision and the cost.

In order to prevent the bending strain generated in the valve shaft 3from being included in the signal obtained from the stain detector 12which is intended for detecting the twist of the valve shaft 3, thereare two shaft bearings 6 on each side of the strain detector 12 so as toprevent the bending strain from being transmitted to the strain detector12. It is preferred that the position of the strain detector 12 on thevalve shaft 3 is determined such that the dynamic torque applied to thevalve member 2 is more directly transmitted to the strain detector 12.From this point of view, the strain detector 12 is disposed on a portionof the valve shaft 3 which is comparatively close to the valve member 2across the shaft bearings 6 and the gland packing 7. Such an arrangementenhances the precision of detection of the dynamic torque applied to thevalve member 2.

The rotation of the valve shaft 3 is transmitted to a potentiometer 15as an angle sensor, through a gear 10 formed on the outer peripheralsurface of the valve shaft 3 and a gear 4 meshing with the gear 10.Thus, the potentiometer 15 is capable of delivering a signal indicativeof the amount of rotation of the valve shaft 3 to a valve openingconverter 16 which converts this signal into the degree of the valveopening of the butterfly valve.

In this embodiment, the gear ratio between the gear 4 and the gear 10 isso selected that the angle of rotation of the valve shaft 3 is amplifiedby the factor of two, thus enabling a higher precision of detection ofthe valve opening.

Thus, the gear 10, gear 4, potentiometer 15 and the valve openingconverter 16 in combination provide a valve opening detection means 17.The potentiometer 15 may be incorporated in the actuator 11. It is alsopossible to arrange such that the rotation of the valve shaft 3 istransmitted to a separate potentiometer 15 through other gearsincorporated in the actuator 11.

The use of the potentiometer 15 is not exclusive. For instance, thevalve opening detection means 17 may have a rotary encoder which isconnected to the gear 4 or 10 and which is capable of directly orindirectly measuring the rotation angle of the valve shaft 3 in terms ofthe number of the teeth of the gear 4 or 10. The valve opening detectionmeans 17 may be installed on a portion of the valve shaft 3 which is onthe opposite side of the valve member 2 with respect to the torquedetection means 14. The described constructions of the valve openingdetection means 17 is only illustrative and various other knownarrangements are usable as the valve opening detection means 17. Theconstruction of the butterfly valve of the present invention is shown inthe form of a schematic diagram in FIG. 2.

According to the present invention, it is possible to determine the flowrate of a fluid flowing through the butterfly valve from the dynamictorque Tm output from the torque detection means 14 and the valveopening θm output from the valve opening detection means 17.

The simplest way of determination is to substitute the torque Tm and theopening θm to the formula (2) which expresses the flow rate Q as afunction G of the dynamic torque T and the valve opening θ which ispeculiar to each butterfly valve and which can be determined beforehand.

    Q=G(θ, T)                                            (2)

This operation can be done without difficulty by means of, for example,a desk-top calculator, so that the flow rate Qm can be definitelydetermined in accordance with the measured values of the torque Tm andthe opening θm. Alternatively, a chart showing the values of the flowrate Q in relation to the torque T and the opening θ is preparedbeforehand, so that the flow rate Qm is located on this chart inaccordance with the measured values of the torque Tm and the opening θm.It is thus possible to achieve the first object of the invention by thecombination of the torque detection means 14 and the valve openingdetection means 17.

In this embodiment, the torque Tm derived from the torque detectionmeans 14 and the opening θm derived from the valve opening detectionmeans 17 are input to the flowrate computation means 18. The flow ratecomputation means 18 includes a memory device 19 which is capable ofstoring the aforementioned function G of the formula (2) which ispeculiar to each butterfly valve and which can be determined beforehand.The flow rate computation means 18 also includes an arithmetic operationdevice 20 which comprises the valve of the function G of the formula (2)using the measured values of the torque Tm and the opening θm. Thus, theflow rate computation means 18 computes and outputs the flow rate Qmupon receipt of the measured values of the torque Tm and the opening θm.It is possible to add a correction to the result of the computation byuse of the formula (2) for the purpose of compensation for any deviationattributable to a change in temperature or changes in the factors suchas the viscosity and the specific gravity of the fluid. Such acorrection can be executed without difficulty by storing necessarycorrection data in the memory device 19. The factors such as thetemperature t, viscosity ξ and the specific gravity gr may be input tothe flow rate computation means 18 as externally settable parameters. Itis also possible to arrange such that these factors are automaticallyinput to the flow rate computation means 18 from a thermometer, aviscometer and a gravimeter which are suitably disposed in the flowpassage near the butterfly valve. The factors such as the temperature t,viscosity ξ and the specific gravity gr may be employed as variances ofa function G', rather than the parameters for correction. In such ascase, it is necessary to determine the function G' as shown by thefollowing formula (10).

    Q=G'(T, θ, t, ξ, Gr)                              (10)

Determination of the function G' through an experiment is possiblealthough a greater number of steps is required for the experiment ascompared with the case of determination of the function G.

By storing this function G' in the flow rate computation means 18, it ispossible to obtain a butterfly valve having a function for measuring theflow rate under a variety of conditions. Thus, the butterfly valve ofthis embodiment can be applied to a variety of types of liquids such aswater, alcohol, lubrication oil, fuel oil, petroleum and so forth. Thebutterfly valve also is applicable to various gases such air, combustiongas, fuel gas, steam and so forth, provided that the precision of thetorque detection means is enhanced.

In the illustrated embodiment, the flow rate Qm output from the flowrate computation means 18 is input to the control means 21 in which adesired flow rate Qd is set externally. The external setting of the flowrate Qd may be conducted by a known remote operation means through asuitable tele-communication device or may be done at the site of thebutterfly valve. The control means 21 operates to compute the differencebetween the flow rate Qm and the flow rate Qd and delivers aninstruction to the actuator 11 so as to cause the actuator 11 to rotatethe valve member 2 in such a direction as to reduce the difference.

A description will be given of the operation of this embodiment. Thebutterfly valve is disposed in a portion of the pipe 100 through which afluid to be controlled flows. The fluid such as water, oil or the likeflows through the pipe 100 at a flow rate which is determined by thedifferential pressure of the fluid across the butterfly valve and thedegree of the valve opening of the butterfly valve.

In this embodiment, the valve opening is variable between 0° and 90°.The valve opening of 0° means that the valve member has been rotated tothe position of the minimum opening so that the fluid is allowed to flowonly through a minute gap left between the valve member 2 and the mainbody 1. Conversely, the valve opening of 90° means the state in whichthe valve is fully opened so that the differntial pressure of the fluidacross the butterfly valve is minimized. It is assumed here that thefluid is flowing through the butterfly valve which is set at a desiredvalve opening. The valve opening detection means 17 detects the valveopening and delivers the same as the opening θm. Meanwhile, the torquedetection means 14 detects the dynamic torque which is produced by thefluid and which acts on the valve member 2 so as to tend to rotate thevalve member 2 about the axis of the valve shaft 3 and delivers the thusdetected torque as the torque Tm. Upon receipt of the opening θm and thetorque Tm, the flow rate computation means 18 executes the computationof the function G of the formula (2) or the function G' of the formula(10) so as to determine the flow rate Qm corresponding to the opening θmand the torque Tm, and delivers this flow rate Qm to the control means21. Upon receipt of the flow rate Qm, the control means 21 operates todetermine any difference between the flow rate Qm and the desired flowrate Qd which is externally set and, if there is any difference,delivers an instruction to the actuator 11 so as to enable the actuator11 to actuate the valve shaft 3 in such a direction as to reduce thedifference. Thus, the instruction given by the control means 21 to theactuator 11 is sorted into the following three types:

(a) Instruction for increasing the valve opening is given when thecondition of Qd<Qm is met.

(b) Instruction for reducing the valve opening is given when thecondition of Qd<Qm is met.

(c) No instruction is given when the condition of Qd=Qm is met.

Thus, the described embodiment employs a closed feedback loop whichenables the actuator 11 to operate in such a manner as to cause themeasured flow rate Qm to infinitely approach the desired flow rate Qd.

The instruction delivered by the control means 21 to the actuator 11 isceased when the measured value of the flow rate Qm has become equal tothe flow rate Qd as a result of operation of the actuator 11, so thatthe actuator 11 stops to operate so as to fix the valve member 2,thereby allowing the instant flow rate Qm to be maintained. Any changein the pressure at the upstream side and/or the downstream side of thebutterfly valve causes the flow rate Qm to be changed, even after thecoincidence between the measured flow rate Qm and the flow rate Qd hasbeen achieved. However, the above-mentioned closed feedback loop enablesthe valve opening to be varied without delay to recover the flow rate Qmcoinciding with the flow rate Qd.

As will be understood from the foregoing description, in the illustratedembodiment, the valve member 2 itself functions both as a sensor forproducing a flow rate information and a restriction member whichrestricts the flow of the fluid in accordance with the thus obtainedflow rate information. Thus, the measurement of the flow rate can beconducted directly and at a high degree of precision without sufferingfrom any error which may otherwise be caused by spacing between thesensor and the butterfly valve and by a delay of time.

A description will be given hereinunder of the manner of setting of thefunction G used in this embodiment. The function F appearing in theformula (1) is well known and the following formula (11) is used as apractical form of the function F. ##EQU1##

In the formula (11), α represents a correction coefficient employed forthe purpose of compensation for a change in the result of measurementcaused by a change in factors such as specific gravity, viscosity andtemperature of the fluid. Thus, the flow rate Q is in proportion to theroot of the differential pressure ΔP, if the opening θ is fixed, and theproportion constant is α×Cv, as can be seen from the formula (11).

Examples of the relationships expressed by the formulae (11) and (5) areshown in FIGS. 3 and 4, respectively. The illustrated embodiment assumesthe relationship expressed by the formula (11). This embodiment alsoassumes the condition of the following formula (12) as to therelationship between the torque T, the opening θ and the differentialpressure ΔP. ##EQU2##

In formula (11), β represents a correction coefficient employed for thepurpose of a compensation for a change in the result of measurementcaused by a change in factors such as specific gravity, viscosity andtemperature of the fluid. Thus, the torque T is in proportion to theroot of the differential pressure ΔP, if the opening θ is fixed, and theproportion constant is β×Cu, as can be seen from the formula (12).

Examples of the relationships expressed by the formulae (12) and (6) areshown in FIGs. 5 and 6, respectively.

The following Formula (13) is obtained by eliminating the term of thedifferential pressure ΔP from the formulas (11) and (12). ##EQU3##

The formula (13) means that, if the opening θ is fixed, the flow rate Qis proportional to the torque T and the proportion constant is(α/β)×(Cv/Cu). It is therefore possible to determine the function G(θ,T)by determining, through an experiment, values of ff(θ) and gg(θ) withvarying the opening θ.

An example of the experiment suitably employed for the determination ofthe values of ff(θ) and gg(θ) will be described hereinafter.

A. System and Instruments Used in Experiment

The system and instruments in the following TABLE are employed in theexperiment. Bearings 6 are used for supporting the valve shaft 3. Theinside diameter of the valve casing 1 is determined to be 2 mm greaterthan the outside diameter of the valve member 2. FIG. 7 shows theoutline of the apparatus. A pressure gauge 22 is capable of measuringthe fluid pressure P₁ at the upstream side of the butterfly valve 27,while a differential pressure meter 23 measures the pressure differenceΔP across the butterfly valve 27. The flow rate Q of the fluid flowingthrough the butterfly valve 27 is measured by an electromagneticflowmeter 24. The fluid is supplied by a fluid supply device 25 to thebutterfly valve 27, as well as to a bypass valve 26 which capable ofchanging its opening degree for the purpose of setting a desired flowrate through the butterfly valve 27.

                  TABLE                                                           ______________________________________                                        SYSTEM AND MAJOR INSTRUMENTS                                                  USED IN EXPERIMENT                                                            Names of Instruments Principal Specifications                                 ______________________________________                                        Butterfly        Valve casing 1                                                                            Nominal diameter                                 valve 27                     150 mm                                                            Valve member                                                                              Outside diameter                                                  2           148 mm                                                                        Central type                                                      Actuator II Output torque 20 Kg-m                            Sensor  Torque   Strain detector                                                                           Sampling frequency                                                            10 KHz                                                                        Precision 0.5 percent                                             Torque transdu-                                                                           Analog output type                                                cer for 3K                                                           Valve    Potentiometer                                                                             Precision 0.1 percent                                    opening              Analog output                                            Differ-  Differential                                                                              Precision 0.1 percent                                    ential   pressure meas-                                                                            Analog output                                            pressure uring device                                                         Flow     Electromag- Precision 0.02 percent                                   rate     netic       Analog output                                                     flowmeter                                                    A/D              Consecutive 12 bit. ± 5 V input                           converter        comparison                                                                    conversion type                                                               A/D converter                                                D/A              Current output                                                                            12 bit. 4˜ 20 mA                           converter        type D/A    output                                                            converter                                                    Control/         16-bit personal                                                                           Memory 1 M                                       Recording        computer    byte RAM                                         device                       Recording medium:                                                             hard disk                                        ______________________________________                                    

B. Measuring Method

The values of the torque T, differential pressure ΔP, pressure P₁ andthe flow rate Q are measured for each unit opening θ of the butterflyvalve 27, while controlling the degrees of the opening θ of the bypassvalve 26 and the opening of the butterfly valve 27 by means of a D/Aconverter. The measurement is conducted under the following conditions:sampling frequency 200 Hz; sample number 200 samples/sec; interval ofsetting of the opening θ 0.2 mA; range of setting of the opening θ 20 mAto 4 mA, interval of setting of the bypass valve opening 1 mA; and rangeof setting of the bypass valve opening 20 mA to 10 mA.

Water maintained at a normal temperature is used as the fluid. Themeasurement is executed by sequentially executing the following steps(a) to (g).

(a) To set the valve opening of the bypass valve 26

(b) To set the opening θ of the butterfly valve 27

(c) To measure the torque T, the differential pressure ΔP, the flow rateQ, the pressure P₁ and the opening θ of the butterfly valve

(d) To record the measured data

(e) To repeat steps (b) to (d) 80 times

(f) To execute the process from the step (a) after 80 executions ofsteps (b) to (d)

(g) To repeat step (a) for a predetermined time, thus completing thewhole process.

C. Results of Experiment

The Cv and Cu values in relation to the measured opening θm, obtained asresults of the experiment, are shown in FIGS. 8 and 9, respectively. Inthese Figures, discrete dots represent the values obtained through theexperiment. In this embodiment, the function ff(θ) of a formula (14) andthe function gg(θ) of a formula (15) are determined, respectively, byapplying four-degree approximate expression and five-degree approximateexpression, respectively, to the values of these discrete dots.

    ff(θ)=θ.sup.4 ×A.sub.4 θ.sup.3 ×A.sub.3 +θ.sup.2 ×A.sub.2 +θ×A.sub.1 +A.sub.0 (14)

where,

A₄ : -9.146×10⁻⁵

A₃ : 1.531×10⁻²

A₂ : -4.746×10⁻¹

A₁ : 1.242×10

A₀ : 0.000

    gg(θ)=θ.sup.5 ×B.sub.5 +θ.sup.4 ×B.sub.4 +θ.sup.3 ×B.sub.3 +θ.sup.2 ×B.sub.2 +θ×B.sub.1 +B.sub.0                           (15)

where,

B₅ : 8.540×10⁻¹⁰

B₄ : -1.672×10⁻⁷

B₃ : 1.125×10⁻⁵

B₂ : -3.572×10⁻⁴

B₁ : 4.919×10⁻³

B₀ : -2.588×10⁻²

The functions ff(θ) and gg(θ) are respectively shown in FIGS. 10 and 11.

Thus, in the illustrated embodiment, the Cv and Cu values are determinedas follows for any opening θ as follows.

    Cv=ff(θ)                                             (5)

    Cu=gg(θ)                                             (6)

Therefore, the flow rate Q can be computed from the measured opening θand the measured torque T from the formula (13), without requiringmeasurement of the differential pressure ΔP, insofar as this butterflyvalve 27 or a butterfly valve of the same design as this valve isconcerned.

Although the four-degree approximate expression and the five-degreeapproximate expression are used in the described embodiment, these useof these approximate expressions is not exclusive. For instance, thefollowing formulae (16) and (17), which are approximate expressions oforder n, can be used in place of the formulae (14) and (15). ##EQU4##where A_(j) represents a coefficient of an order j ##EQU5## where B_(j)represents a coefficient of an order j

It is also possible to use known approximate expressions in place of theformulae (16) and (17). The conditions of the experiments such as thesampling frequency, interval of setting of the opening θ and/or theinterval of setting of the bypass valve opening are preferably varied inaccordance with the demanded measuring precision.

Although the conditions of the formulae (11) and (12) are assumed inthis embodiment, such assumption is not essential. Namely, the functionF(θ, ΔP) and H(θ, ΔP) may be determined in accordance with anexperimental formula from the flow rate Q, the opening θ, thedifferential pressure ΔP and the torque T. It is to be noted that thefunction G(θ, T) may be determined as an experimental formula directlyfrom the results of the experiment, although in the described embodimentthe function G (θ, T) is determined after the determination of thefunctions ff(θ) and gg(θ).

It is also possible to form a chart showing the values of the flow rateQ in relation to the opening θ and the torque T from the experimentresult, with the portions between discrete dots interpolated with asuitable interpolation formula, so that the flow rate Q can be read onthe chart in accordance with the measured values of the opening θ andthe torque T.

All these methods for determining the flow rate Q can be performedquickly by making use of a computer.

As has been described, the butterfly valve of the present invention hasa valve opening detection means capable of detecting the degree of thevalve opening of the butterfly valve and a torque detection meanscapable of detecting the dynamic torque produced by the flow of thefluid acting on the valve member around the axis of the valve shaft.Therefore, by determining beforehand a relationship between the flowrate and the values of the valve opening and the dynamic torque peculiarto the butterfly valve, it is possible to determine the flow rate fromthe measured values of the valve opening and the dynamic torque. Thus,in the butterfly valve of the present invention, the valve member hasnot only a function for restricting the flow of the fluid but also afunction for sensing the flow rate. It is therefore possible to directlymeasure the flow rate of the fluid passing through the butterfly valvewithout error which may otherwise be caused due to a positionaldifference and time delay when the flow rate is measured by a separateflowmeter. The higher precision of measurement of the flow rate thusattained ensures higher speed and precision of the control of the flowrate conducted in accordance with the flow rate information. The flowrate measurement which does not rely upon conductivity of the fluidenables the butterfly valve to be used in controlling the flow rate of anonconductive fluid such as an oil. In addition, the control of the flowrate of the fluid can be done without disposing any flowmeter in theflow passage other than the butterfly valve.

Many widely different embodiments of the present invention may beconstructed without departing from the spirit and scope of the presentinvention. It should be understood that the present invention is notlimited to the specific embodiments described in this specification,except as defined in the appended claims.

What is claimed is:
 1. A butterfly valve having as one function themeasurement of a flow rate of a fluid flowing through said butterflyvalve, comprising;a main body, a valve shaft fixed rotatably to saidmain body, a valve member fixed to said valve shaft and mountedrotatably in said main body, a valve opening detection means fordetecting a valve opening of said butterfly valve, a torque detectionmeans for detecting a dynamic torque applied to said valve member aroundsaid valve shaft by said fluid, and a flow rate computation means forcomputing said flow rate as a predetermined function of said valveopening and said dynamic torque.
 2. A butterfly valve according to claim1, further comprising an actuator connected to said valve shaft forrotating said valve member.
 3. A butterfly valve according to claim 2,in which said actuator is selected from a group consisting of anelectric actuator, a pneumatic actuator, a diaphragm-type actuator and asolenoid-type actuator.
 4. A butterfly valve according to claim 2,further comprising a control means at which a desired flow rate can beexternally set and which instructs said actuator to rotate said valvemember such that said computed flow rate approaches said desired flowrate.
 5. A butterfly valve according to claim 4, in which said desiredflow rate can be set to said control means from a remote place by aremote operation means through a tele-communication means.
 6. Abutterfly valve according to claim 1, in which said torque detectionmeans includes a strain detector provided to said valve shaft.
 7. Abutterfly valve according to claim 1, in which said valve openingdetection means includes an angle sensor connected to said valve shaft.8. A butterfly valve according to claim 7, in which said angle sensorcomprises a potentiometer or a rotary encoder connected to said valveshaft.
 9. A butterfly valve according to claim 1, characterized in thatsaid butterfly valve is a central-type or an eccentric-type.
 10. Amethod of measuring a flow rate of a fluid flowing through a butterflyvalve, comprising the steps of;detecting a valve opening of saidbutterfly valve, detecting a dynamic torque applied to a valve member ofsaid butterfly valve around a valve shaft of said butterfly valve bysaid fluid, and determining said flow rate as a function of saiddetected valve opening and said detected dynamic torque.
 11. A methodaccording to claim 10, in which said function is estimated by obtaininga relationship between said flow rate and said valve opening and saiddynamic torque through an experiment.
 12. A method according to claim10, in which said function is estimated on an assumption that said flowrate is proportional to said dynamic torque when said valve opening isunchanged.
 13. A method according to claim 10, in which said flow rateis determined on a chart which shows a relationship between said flowrate and said valve opening and said dynamic torque.
 14. A methodaccording to claim 13, in which said relationship is obtained through anexperiment.
 15. A method according to claim 10, in which determinationof said flow rate is executed by a computer.
 16. A method of controllinga flow rate of a fluid flowing through a butterfly valve, comprising thesteps of:detecting a valve opening of said butterfly valve detecting adynamic torque applied to a valve member of said butterfly valve arounda valve shaft of said butterfly valve by said fluid, detecting said flowrate as a function of said detected valve opening and said detecteddynamic torque, setting a desired flow rate, and changing said valveopening such that said determined flow rate approaches said desired flowrate.